1. Field of the Invention
The present invention relates to a method for making a water redispersible epoxy polymer powder and the resulting water redispersible epoxy polymer powder and dispersions of epoxy polymer particles.
2. Description of Related Art
Water redispersible polymer (RDP) powders are dry powders of polymer particles that upon mixing with an aqueous fluid dissociate and form a polymer dispersion in the aqueous fluid. Water RDP powders of polymeric binders are valuable additives in dry formulations of cementitious materials such as mortar, grout and concrete for the purpose enhancing final properties of the resulting material. Epoxies, for example, are desirable additives in cementitious formulation to increase toughness, reduce water permeability and/or increase chemical and stain resistance in cementitious materials. Epoxies can be added to a cementitious formulation as a liquid dispersion. However, it is desirable to include epoxy additives in the form of a water RDP powder to dry cement formulations for convenience in shipping, formulating and handling. RDP powders of epoxy resins are not well known despite a desire for such a material. Those RDP powders containing epoxy resins that do contain epoxy polymer comprise a minor amount (50 wt % or less) of epoxy resin blended into another polymer (typically emulsion polymerized) polymer.
United States published patent application 20100197831A1 discloses a water redispersible powder of a polymer combination that comprises up to 50 wt % epoxy polymer. The polymer powder is prepared by emulsion polymerizing a non-epoxy polymer, then adding epoxy resin to the emulsion polymer and isolating the resulting polymer blend particles as a powder.
United States published patent application 2001/0024644 discloses a method for preparing a dispersion of polymer particles by emulsion polymerization of monomers, up to 10 percent by weight of which can contain epoxy functionality and incorporating into the emulsion particles up to 50 wt % of an non-copolymerizable difunctional epoxy. The resulting emulsion particles can be isolated to form a water redispersible polymer powder.
European patent application EP723975A1 discloses a water redispersible polymer powder that comprises a copolymer that contains up to 50 percent by weight of epoxide-group containing ethylenically unsaturated comonomer.
Lacking from these references is a method for forming a RDP powder that contains greater than 50 wt % epoxy resin based on RDP particle weight. Such a RDP powder would be desirable for concentrated delivery of epoxy resin in dry powder form. Further lacking from these references is a method forming a RDP powder that contains greater than 50 wt % epoxy resin based on RDP powder particle weight where the epoxy resin has a glass transition temperature below the temperatures at which it is isolated as a RDP powder or even more below temperatures at which is it used, or a method for preparing such a RDP powder. Such RDP powders would be highly desirable for concentrated delivery and quick dissociation of epoxy into cementitious formulations.